I'm working on a project for my camera. I need to be able to release water drops at the precise times, an example of this would be this setup from glacialwanderer:

http://www.glacialwanderer.com/hobbyrobotics/?p=407

The problem is I cannot get hold of one of these solenoids anytime soon, and it will be pretty expensive. I have tried making a device using a speaker that would "pump" the water out from source above into a syringe head below. Attached is a rough drawing. This is working fine for air, however because of the flexibility of the speaker's membrane the vacuum is quickly lost and the water just flows out. I also don't have the tools needed to make the necessary components for an actual solenoid valve. Has any one faced this kind of problem before? Any ideas how I could get this to work with water?

@ JacobChrist: I have tried that and it works to an extent, the problem is once the surface tension is broken I can't seem to get it to stop slowing. I am about to try making the surface tension stronger by adding salt to the water, I really hope that this does it!

@ pantonvich: I have a s trap in the tube from the supplying syringe to the lower dam. It has helped but not completely. Are you saying the motor would then screw the threaded rod into the nut to close, and out to open? I am not sure this would be fast enough as the purpose is for the water drops to collide. But nice idea

I have tried making a device using a speaker that would "pump" the water out from source above into a syringe head below. Attached is a rough drawing. This is working fine for air, however because of the flexibility of the speaker's membrane the vacuum is quickly lost and the water just flows out.

You could just put a piece of plastic wrap between the speaker and vessel so it is no longer air permeable.

What about a servo connected directly to the plunger of the syringe? Or a linear actuator, like a stepper motor and ready rod.

Or a stepper motor connected to a roller, pinching a long tube full of water. Similar to the medical thumb roller method that was mentioned in your link? [url]http://www.glacialwanderer.com/hobbyrobotics/?p=407#comment-9184 [\url]

Thought 1 was to set up something that would drip at a constant slow frequency and either predict, or detect electronically, when a drip is falling so that you can trigger whatever it is you want to do.

Thought 2 was that inject printers work by spraying extremely small amounts of ink at moderate speed and perhaps an inkjet head could be adopted to shoot tiny water droplets on demand.

I only provide help via the forum - please do not contact me for private consultancy.

@ MonkeyKnight: That might work well! I'm going to give that a try during the day and let you know how well it works.

@ PeterH: The drops have to be fairly large, I already have a system for single drops. I have an Arduino set up with light, sound and vibration senors. Depending on the light generated from the action I am trying to capture the shutter is either left open in a dark room and the flashes are triggered via the sensors. If there is a lot of light I have an IR LED which triggers the shutter. In this particular case I am trying to get easy collisions. Here is a link:

Solenoids usually are electromagnets that are optimised for long travel distance.

If you can get a reasonably-sized relay you may be able to use it's mechanical movement.

Every automobile has several small plug-in relays, "headlight relays" etc. They run on 12 VDC. Find a scrap yard. I would not recommend *Midnight Auto unless you are under the age of 12...

EDIT: * Sorry, dumb wise*** comment. "Midnight Auto", back in the 50's was stealing needed car parts from some other car, around Midnight. If you were caught but were underage, you didn't go to jail... Sigh...

Thanks for the help! Luckily I managed to find a far larger syringe for the top, one that is used to medicate livestock, my device now works pretty well and using the Arduino I can now control drop collisions with less trouble! And avoided ordering a solenoid

@ terryking228: Thanks! I will defiantly have a look into that next time. I am not sure I understand what you mean about the age thing?